Scientists at Wisconsin are working on ways to kill just one species of bacteria. They are starting with C. diff, but the technology could potentially be used for any bacteria. From Futurism.com:

Jan-Peter van Pijkeren, a food scientist from the University of Wisconsin-Madison, is creating a probiotic cocktail that patients can swallow as a liquid or pill.

The cocktail of bacteria will include a bacteriophage – a virus that infects bacteria – capable of carrying a customized, false, CRISPR message to C. difficile. This message would cause C. difficile to make lethal cuts to its own DNA.

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“The downside of antibiotics is they are a sledgehammer that depletes and destroys the gut microbial community,” van Pijkeren said to the University of Wisconsin-Madison. “You want to instead use a scalpel in order to specifically eradicate the microbe of interest.”

CRISPR is ideal for this use because such drugs would be very specific to the user. They could kill a single species of germ while leaving good bacterial untouched. In contrast, regular antibiotics kill off both good and bad bacteria, leading to resistance. If proven successful, CRISPR could become, not just the world’s most effective gene editing tool, but also the best bacteria-killing technology available.